High-resistance SNS sandwich-type Josephson junctions

Abstract

We have investigated the behavior of SNS and SIS junctions with barriers in the vicinity of the Metal-Insulator (M/I) transition. We use Nb for the superconductor and amorphous-(Nb-Si) for the barrier. All junctions were made by means of electron-beam evaporation on Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> substrates. The junction areas were defined by the Selective Niobium Anodization Process (SNAP). We have made junctions down to 8 × 8 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and barrier thicknesses in range from 250 Å to 600 Å. The composition of the barrier was varied from 5 % Nb to 15 % Nb. Working on the metallic side of the M/I transition we observe μ-bridge-like I-V characteristics with R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</inf> A <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim0.3 \Omega-\mu</tex> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</inf> <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim 200 \mu</tex> V.